Genesis 21:3

“And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.”

KJV

Meaning

Naming the child Isaac identifies him with the promise already announced and continues the chapter's emphasis on fulfillment.

The name participates in the literary theme of laughter, but the verse does not require one single psychological meaning for every earlier laugh.

Names can carry memory and meaning; here the name keeps the surprising fulfillment of promise in view.